The present invention relates to a shadow mask type color picture tube.
It is generally well known that a shadow mask of a shadow mask type color picture tube is locally expanded due to its thermal expansion, and a landing error of electrons passing therethrough occurs. Such local expansion of the shadow mask is called doming. The doming phenomenon typically occurs when the shadow mask becomes flat. When the shadow mask has a smaller radius of curvature, doming is reduced. Various countermeasures have been conventionally implemented to reduce doming. For example, the aperture pitch in a shadow mask is increased from the central portion toward the periphery. By adapting such a variable pitch technique, the radius of curvature of the shadow mask as a whole is decreased to reduce the doming phenomenon. In this conventional structure, however, since the shadow mask as a whole is fabricated in accordance with the variable pitch technique, an image at the peripheral portion of the screen has a poor resolution when a difference between the pitch of the central and peripheral apertures becomes large. For this reason, an increase in the pitch of the peripheral apertures is limited within an allowable image quality.
In addition, demand has recently arisen for high-resolution color picture tubes for displaying small characters. In order to meet this demand, the pitch of the apertures in the shadow mask must be decreased. However, when this demand is satisfied, the doming phenomenon cannot be eliminated if only the variable pitch technique is adapted.
Furthermore, there is also a tendency for flattening of the phosphor screen of a color picture tube. This tendency conflicts with demand for preventing the doming phenomenon.